1. Field of the Disclosure
The present disclosure relates to a curable composition comprising one or more polymers having a silicon-containing group which has a hydroxyl group or hydrolyzable group bonded to a silicon atom and can form a siloxane bond to be crosslinked (said silicon-containing group may be referred to as a “reactive-silicon-containing group” hereinafter).
2. Description of the Related Art
It has been known that organic polymers, with at least one reactive silicon group can polymerize with the formation of siloxane bond by hydrolysis and/or condensation reactions aided by moisture and suitable catalysts even at room temperature, whereby the polymers are crosslinked to give a fully cured product.
Among these polymers having a reactive silicon group, polymers wherein the main chain skeleton thereof is a polyoxyalkylene polymer or polyisobutylene polymer are well known and these polymers are already produced industrially, and are widely used in sealants, adhesives and paints. The curable composition used in sealants, adhesives, or the like, are required to have various desirable attributes such as curability, adhesiveness, and mechanical property.
Polymers having reactive terminal silyl groups or compositions comprising such polymers can be hydrolyzed and condensed in the presence of water and organometallic catalysts. Suitable known catalysts for curable compositions include organometallic compounds employing metals such as Sn, and Ti. Organotin compounds such as, for example, dibutyltin dilaurate (DBTDL), and dibutyltin bis(acetylacetonate) are widely used as condensation cure catalysts to accelerate the moisture assisted curing of a number of different polyorganosiloxanes and non-silicone polymers having reactive terminal silyl groups such as room temperature vulcanizing (RTV) formulations including RTV-1 and RTV-2 formulations. Environmental regulatory agencies and directives, however, have increased or are expected to increase restrictions on the use of organotin compounds in formulated products. For example, while formulations with greater than 0.5 wt. % dibutyltin presently require labeling as toxic with reproductive 1B classification, dibutyltin-containing formulations are proposed to be completely phased out in consumer applications during next several years.
Alternative organotin compounds such as dioctyltin compounds and dimethyltin compounds are only short-term remedies, as these organotin compounds may also be regulated in the future. It would be beneficial to identify non-tin metal catalysts that accelerate the condensation curing of moisture curable silicones and non-silicones. Desirably, substitutes for organotin catalysts should exhibit properties similar to organotin compounds in terms of curing, storage, and appearance. Non-tin catalysts should also initiate the condensation reaction of the selected polymers and complete this reaction at the surface and in the bulk within a desired time frame.
The use of zinc complexes as catalysts in condensation curable silicone compositions has been described. For example, U.S. Patent Publication Nos. 2011/0046304 and 2009/0156737; WO 2010/146253; and EP 1178150 describe the use of zinc compounds for silyl condensation cure chemistry.
U.S. Pat. No. 5,985,991 broadly claims the use of various metals in a generic list of metal acetylacetonates consisting of Cu, Cr, Al, Zn, Ti, and Zr to improve the oil resistance of RTV silicone composition which comprises metal salt of carboxylic acid as a condensation cure catalyst.
U.S. Pat. No. 5,945,466 broadly claims a generic list of organic metal compounds containing Sn, Ti, Zr, Pd, Zn, Co, Mn and Al as metallic element, as curing catalyst for room temperature curable organopolysiloxane composition which contains organosilane or its hydrolyzed product among other components.
U.S. Pat. No. 7,365,145 generically claims, a generic list of organic dibutyltin, zirconium complex, aluminum chelate, titanium chelate, organic zinc, organic cobalt, and organic nickel as catalysts in moisture curable silylated polymer composition.
U.S. Publication No. 2009/0156737 claims a generic list of Lewis acid compounds of Ti, Zr, Hf, Zn, B, Al as catalysts in polymer blends comprising alkoxy silane terminated polymers and fillers.
U.S. Pat. No. 4,293,597 includes a generic list of metal salts including Pb, Sn, Zr, Sb, Cd, Ba, Ca, and Ti as catalysts in curable silicone rubber compositions that also contains nitrogen-functional silanes.
U.S. Pat. No. 4,461,867 includes a generic list of metal esters also including Sn, Pb, Zr, Sb, Cd, Ba, Ca, Ti, Mn, Zn, Cr, Co, Ni, Al, Ga and Ge as a catalyst in moisture curable RTV-1 silicone compositions.
U.S. Patent Publication No. 2011/0098420 includes a generic list including compounds of Pt, Pd, Pb, Sn, Zn, Ti and Zr, as dehydrogenative condensation reaction catalyst for a curable polysiloxane composition comprising of siloxanes with 2 or more hydrosilyl groups and siloxanes with 2 or more silanol groups.
U.S. Pat. No. 7,527,838 claims a generic list of materials which includes metal catalysts based on Sn, Ti, Zr, Pb, Co, Sb, Mn and Zn, in curable diorganopolysiloxane compositions used for making insulated glass units.
Despite these general teachings, there has not been provided any teachings or catalyst compositions that improve on the catalytic activity exhibited by synergistic mixtures of different metal amidine complexes and carboxylate salts of various amines. Further, there has not been a replacement catalyst for organo-tin compounds that maintains its ability to cure after storage over months in a sealed cartridge, when exposed to humidity or ambient air. It is always a specific requirement for moisture curable compositions to achieve the shortest possible curing times, showing a tack-free surface as well as a curing through the complete bulk in thick section for “One-Part” and “Two-Part” Room-Temperature Vulcanizing (RTV) compositions and provide a reasonable adhesion after cure onto a variety of substrates.
JP-A-5-117519 discloses that the curing performance is abruptly improved by using a carboxylic acid and an amine together, but these compositions suffer from lack of sufficient adhesiveness. In addition, storage stability of such catalysts is undesirable and premature gelation can occur during storage of such compositions.